Electric valve circuit



1944- o. w. LIVINGSTON 2,355,453

ELECTRIC VALVE C IRCUI T Filed Dec. 18, 1941 H 2 Inventor:

OTTinW Ljvin ston,

Fawn '3 1 His Attorneg.

Patented Aug. 8, 1944 ELECTRIC VALVE CIRCUIT Orrin W. Livingston,Scotia, N. Y., assignor to General Electric Company, a corporation ofNew York Application December 18, 1941, Serial No. 423,522

12 Claims.

My invention relates to electric valve translating apparatus, and moreparticularly to control or regulating circuits ior electric valvesystems.

Electric valve apparatus oflers decided advantages in those applicationswhere it is desired to effect energization of a load circuit, such as awelding circuit, for a predetermined interval of time or forpredetermined recurring intervals of time, and where it is desired toellect the transmission of a precise amount of current to the loadcircuit during such intervals. In accordance with the teachings of myinvention discussed hereinafter, I provide a new and improved control orregulating system which is susceptible of controlling the amount ofcurrent transmitted to a load circuit in a more precise manner than thatafforded by the prior art arrangements.

It is an object of my invention to provide a new and improved electrictranslating system.

It is another object of my invention to provide a new and improvedelectric valve control system for electric translating apparatus.

It is a further object of my invention to provide a new and improvedcontrol or regulating system for electric valve apparatus wherein anelectrical condition, such as the current of the load circuit, isprecisely maintained at a definite value.

It is a still further object of my invention to provide a new andimproved regulating system for electric translating apparatus which maybe operated intermittently to effect energization of the load circuitduring predetermined intervals of time.

Briefly stated, in the illustrated embodiment of my invention I providea new and improved control or regulating system for maintaining anelectrical condition, such as the current of a load circuit, preciselyat a definite value. The electric translating apparatus is controlled toeiiect intermittent energization of the load circuit duringpredetermined intervals of time, and the control or regulating circuit,which is responsive to the load current, controls the conductivity ofthe electric translating apparatus to maintain the load constant. Meansare provided in the control or regulating circuit to control the rangeof control obtainable and to assure that the load current is maintainedat a definite value during each energization including the first halfcycle of energization oi the load circuit. I r

In some. applications of electric valve converting systems toarrangements 'for energizing load or regulator which permits accuratecontrol of the current transmitted to the load circuit and to compensatethereby for variations in impedance or inductance of the load circuit,For example, in many welding machines the inductance of the secondarywinding of the power transformer which is connected to the arms of thewelding machine is varied due to the adjustability of the welding arms.In accordance with my invention, I provide a regulator which adequatelycontrols the load current irrespective of variations in the inductanceof the welding transformer circuit occasioned by the adjustment of thewelding machine.

For a bettenunderstanding of my invention, reference may be had to thefollowing description taken in connection with the accompanying drawing,and its scope will be pointed out in the I appended claims. The singlefigure of thedrawing diagrammatically illustrates an embodiment of myinvention as applied to an electric valve translating system forenergizing a welding circult.

Referring now to the single figure of the drawing, I have thereillustrated my invention as applied to an electric translating systemfor energizing a load circuit, such as a welding circuit I, from analternating current supply circuit 2 through electric translatingapparatus including a transformer I and a pair of reversely connectedelectric valve means 4 and 5. A suitable circuit controlling means orswitch 6 may be connected between the supply circuit 2 and thetranslating apparatus.

The electric valve means 4 and 5 are preferably of the type comprisingan ionizable medium, such as a gas or a vapor, and each may comprise ananode l, a cathode, such as a mercury pool cathode 8, and a controlmember 9 which may be of the immersion-ignitor type having an extremitythereof extending into the mercury of the associated cathode. Thecontrol members 9 are constructed of a material such as boronrespectively, and which comprise trigger or con- ,trol electricdischarge devices l2 and I3. These electric discharge devices arealsopreferably of the type employing an ionizable medium, such as -,agas or a vapon-and eachmay'comprise an circuits, such as weldingcircuits and welding ma? chines, it is necessary to provide a controlsystem anode, a cathode", a cathode heating element: is andtcontrolmeans. The control means control member or shield grid i8 which may beconnected to the cathode II. Excitation circuits i and I I may comprisemeans for impressing on the grids i1 negative unidirectional biasingpotentials and may include self-biasing means, such as a parallelconnected resistance It and a capacitance 20. Filtering capacitances 2|and 22 may be connected in the excitation circuits ll and H in order toabsorb extraneous transient voltages present therein. The electricdischarge devices i2 and ii are arranged to be responsive to thepolarity of the anode-cathode voltages of the respective associated mainelectric valves (and 5, and are connected between the anodes I andcontrol members 9 thereof through current limiting resistances 23 and2|, respectively.

As a means for impressing hold-oil voltages on the control grids ll ofthe electric discharge devices 12 and i3, I provide a transformer 25having a primary winding 26 and secondary windings 21 and 28.Capacitances 28 and 30 may be connected across the secondary windings 21and 28, respectively. The transformer 25 is also provided with secondarywindings 3| and 32 which serve as sources of cathode heating current forthe cathode heating elements I of electric discharge devices 12 and i3.An auxiliary source of alternating current may be provided by means of asecondary winding 33, the function of which is explained hereinafter.

To superimpose on the biasing or hold-off voltages impressed on controlgrids ll of electric discharge devices i2 and I2, voltages to determinethe periods of conduction of the electric discharge devices I2 and II,but which are of a value in themselves insufficient to overcome theeffect of the biasing voltages, and which require the presence ofadditional voltages such as voltages of peaked wave form, describedhereinafter, I provide a transformer 34 having a primary winding 35 andsecondary windings 26 and I! which are connected to the grids I! ofelectric discharge devices I 2 and II, respectively.

I employ a transformer 31 comprising a primary winding 39 and secondarywindings 40 and H which impress on the grids I! of the electricdischarge devices I2 and II, respectively, alternating voltages ofpeaked wave form which, cooperating with the voltages produced bysecondary windings 36 and I! of transformer ll, render the electricdischarge devices l2 and II, and hence the main or power electric valvemeans 4 and 5, conducting during predetermined intervals of time such aspredetermined numbers of half cycles of voltage of supply circuit 2.

A timing circuit 42 is provided which produces a timing voltage andwhich accordingly determines the period of conduction of electric valvemeans 4 and 5, thereby determining the period of energization of thewelding circuit I. The timing voltage is controlled to render theelectric valve means 4 and conducting for a predetermined number of halfcycles of voltage of the supply circuit 2. The timing circuit 42 comprises a, suitable source of direct current 48. This source of directcurrent may be provided by means of a rectifier M which may be of theiii-phase type comprising a transformer 45 and pair of unidirectionalconducting paths provided by a rectifying device 45. Transformer 45 isprovided with a winding 41 which is connected to the rectifying devicel6, and may also be provided with secondary windings l8 and I! whichserve as sources or cathode heating current. Primary winding 50 oftransformer 45 is connected to circuit 5 I which is energized from asecondary winding II of transformer II. A suitable filtering inductanceN and a capacitance ll may be connected across the direct current source48.

To produce a timing voltage. I employ a capacitance II which isconnected to be charged from the direct current source 43 through aportion of a resistance 51 and a control electric valve 5|. Th controlelectric valve 52 is preferably of the type employing an ionizablemedium and comprises a control grid 58. Electric valve 58 is renderedconducting precisely at a predetermined time during cycles of voltage ofcircuit 2 or circuit Si by means of a transformer which may be of thesaturable type designed to produce a voltage of peaked wave form.Transformer i0 includes a primary winding I and a secondary winding 62which is connected to grid 59 through a resistance 63. A variableimpedance, such as a variable resistance ll, may be connected in seriesrelation with primary winding SI of transformer 60 in order to controlthe phase of the output voltage of peaked wave form with respect to thevoltage of circuit ii. In order to control the magnitude and the waveshape of the timing voltage produced by circuit 42, I employ aresistance or a plurality of resistances CF10, inclusive, having aplurality of taps llinclusive, and which are connected across the source43. The eflective value of resistances "-10, inclusive, may becontrolled by means of resistances 15-11 and by means of associated gangswitches ll-80, inclusive.

To initiate operation 01' the timing circuit 42, I provide an initiatingswitch it. Switch II is connected in circuit with an actuating coil .8of relay 83 which is provided with contacts II in series relation withthe anode-cathode circuit of the control electric valve 5!, and is alsoprovided with contacts 85 which close a discharge circuit for thecapacitance 56.

As an agency for supplying to the transformer 34, particularly primarywinding 35 thereof, a predetermined number of half cycles of currentcorresponding to the desired period of margintion of the welding circuit0 determined by the timing voltage produced by timing circuit 42, Iprovide electric valve means such as a pair of coupling or controlelectric discharge devices II and 81. These discharge devices arepreferably of the type employing an ionizable medium and each includes acontrol grid II. The anodecathode circuits of the discharge devices IIand 81 are connected reversely in parallel so that alternating currentis transmitted to the primary winding 35 of transformer 34 from circuitI. The electric discharge devices I! and .1 may be arranged in a leadingand trailing relationship; that is, the electric discharge device ll maybe controlled in response to the timing voltage pro-- duced by circuit42 through conductor IO, and the electric discharge device l1 may beconnected to conduct current in response to the conductivity or currentconducted by discharge device 2.. This control may be obtained by meansof a transformer having a primary winding SI and secondary windings 92and 93. Secondary winding 92 is connected to impress an alternatingcomponent of voltage on grid 88 of discharge device 86 throughresistances 94 and 95; and the secondary winding 83 is connected to gridll of the discharge device I! to impress a relatively positive voltageon grid 88 in response to the conductivity of the discharge device N. Asuitable source of self-biasing potential, such as a parallel connectedcapacitance and a resistance 01, may be connected to the grid 00 of thedischarge device 01. A current limiting resistance 00 and a capacitance00 may be connected in series relation with primary winding II oftransformer 00. This means serves to prevent the imposition of asubstantial lagging current on circuit II when the electric dischargedevices 00 f and 01 are rendered conducting, and also serves to obtainthe desired phase displacement between the voltages produced bysecondary windings 92 and 90 relative to the voltage of circuit Atransformer I00 having a primary winding IOI and a secondary winding I02is employed to impress a hold-off voltage on the grid 00 of dischargedevice 8I. Of course, after the discharge device 00 conducts, thevoltage produced by winding 90 is sufficient to render the dischargedevice 01 conductive by overcoming the effect of the voltage produced bya winding I02. A capacitance I03 may be connected across the terminalsof winding I02. windings I04 and I00 of transformer I00 may be used assources of cathode heating current for discharge devices 00 and 01 Themagnitude of the voltage produced by secondary winding I02 is sufficientto maintain the discharge device 81 non-conducting when transformer 90is not energized. However, when transformer 190 is energized, thevoltage produced by secondary winding 00 is suflicient to overcome theetfectof the winding I02 and the discharge device 01 is renderedconducting.

I employ protective means, such as time delay apparatus, for preventingoperation of the system until the cathodes of the various electricdischarge devices have attained safe operating temperatures. Forexample, I provide a time delay relay I00 having an actuating coil I01and contacts I00. Actuating coil I0'I is connected to be energized fromcircuit 0| through transformer I00. After a'predetermined time delay,contacts I00 are closed. I also provide another protective relay I09having an actuating coil III! and contacts I I I and I I2 which areconnected in the anode-cathode circuits of the. control electricdischarge devices I2 and I0, respectively. This relay prevents closureof the excitation circuits until after operation of the time delay relayI00.

To control the amount of current transmitted to the load circuit Iduring each period of energization of the welding circuit I, I providemeans exclusively electrical for controlling the phase relationship ofthe voltages of peaked wave form impressed on grids II of electricdischarge devices I2 and I3 by means of transformer 00. Morespecifically, I connect suitable phase shifting means, such as phaseshifting means of the static impedance type which may be energized fromthe secondary'winding of transformer 02. The phase shifting circuit maybe of the bridge type wherein one branch oi the bridge comprises acapacitance H0 and a resistance H4, and in which the other branch of thebridge comprises a resistance I I0 and a variable impedance element suchas a variable inductance which may comprise a transformer IIO having awinding III connected in the bridge circuit and provided with a windingIIO which is controlled to vary the effective inductive reactance ofwinding III. A variable resistance II! may be connected in seriesrelation with the winding I, if desired. Suitable means, such as anadjustable resistance I20, may be connected across the winding II I,

or across winding III and resistance IIO, to 70 limit the possible rangeof phase shift of the alternating voltage supplied to transformer 00and, hence, to limit the phase of the peaked voltages produced bywindings 40 and 4| of this transformer.

Resistances III and I20 together limit the amount of phase shiftproduced by maximum and minimum conductivity of valves I2I and I22 andthereby minimize any tendency of the system to hunt while stillpermitting suflicient range of operation to maintain th load current ata constant value under actual operation.

The effective inductive reactance of winding II'I may be controlled bymeans such as a pair of electric discharge devices I2I and I 22, eachbeing provided with a control grid I20. The discharge devices I2I andI22 are arranged to transmit variable amounts of current through windingIIO, thereby controlling the effective inductive reactance of windingIII. I provide means responsive to the current transmitted between thesupply circuit 2 and load circuit I for controlling the phase positionof the voltages of peaked wave form which are impressed on grids I! ofdischarge devices I2 and I0, thereby maintaining the current transmittedto welding circuit I at a substantially constant value. A rectifler I24energized from a current transformer I20 and comprising rectifying meanssuch as unidirectional conducting paths I20 produces across a resistanceI21 and a capacitance I20 a unidirectional voltage the magnitude ofwhich varies in accordance with the magnitude of the current transmittedbetween the supply circuit and the welding circuit. A smoothingreactance I20 may be connected in series relation with the output of theconductingpaths I20, and a voltage limiting means such as a resistanceI00 may be connected across the output terminals of the currenttransformer I20.

In order to control the potential of the grids I20 of electric dischargedevices I2I and I22, I employ a control circuit IOI which is exclusivelyelectrical and which employs no moving parts. The control circuit IOIcomprises a source of unidirectional voltage I02 of substantiallyconstant value which may be provided by means of. a rectifier I00including a rectifying device I04 energized from secondary winding 00 oftransformer 20. Suitable filtering means including capacitances I00 andsmoothing inductance I00 are connectedacross the output circuit of therectifier I00. Circuit IOI also includes an electric discharge deviceI01, the anode-ca thode circuit of which is energized from the directcurrent source I02 through a resistance I00, and a suitable constantvoltage device, such as a glow discharge valve I00, which is of the typewhich maintains across its terminals 9. substantially constant voltagewhen maintained in an ionized or conducting condition. Discharge deviceI0! is provided with one control grid I40 and a second control grid MI.The potential of grid I is varied in accordance with the output voltageof rectifier I24, and thereby accurately and precisely controls theamount of current transmitted through resistance I00 to control thepotential of grids I20 in response to the current transmitted betweenthe supply circuit and the welding circuit.

The potential of grid I4I varies in response to the voltage appearingacross resistance I2I. Grid I40 is energized from a voltage dividerconnected between the positive and negative terminals of the right-handcapacitance I00. This voltage divider comprises resistances I42 and 3.Grid ill is connected to the positive terminal of resistance I21 througha resistance I.

I provide current pre-set means, such as an electric discharge device Ihaving an anodecathode circuit connected in parallel with the anode andcathode of discharge device I31 and which controls the voltage impressedon grids I23 during and preceding the initiation of each period ofenergization of welding circuit I, thereby limiting the phasedisplacement between the voltages of peaked wave form impressed on gridsll of discharge devices I! and I3 and, consequently, limiting orpre-setting the maximum amount of current which may be transmitted tothe welding circuit i during such times of initiation. Discharge deviceI" includes screen grid I", which may be energized from the voltagedivider, including resistances Ill and Ill. Control grid I46 isconnected across the resistance I21 through a voltage divider includingresistances I and I. Resistances I and I are proportioned so that whenthis voltage divider circuit is closed, the voltage impressed on grid Iis suiiiciently positive to maintain the discharge device Illconductive, thereby maintaining the potential impressed on grids I21sufflciently negative so that these discharge devices are maintained ata small degree of conductivity or completely biased to cut-off.

While the discharge devices Ill and I2! may be controlled by circuit Illso that these discharge devices are biased to cut-off, it will beunderstood that the circuit III may be adjusted so that theconductivities of the discharge devices IM and I12 are varied withinsuch limits as to produce only a minimum disturbance of the systemduring the initiation 01' each energization of the load circuit and atthe same time provide an adequate control thereof to prevent thetransmission of either an excessively large or exceedingly small valueof load current at the beginning of each energization of the loadcircuit.

I provide means, such as current responsive means, for initially biasingthe circuit ill and the excitation system, so that a current in excessof a predetermined maximum current may not be transmitted to weldingcircuit l during the initiation of each period of energization. Thisbiasing means may comprise a relay I50 having an actuating coil which isenergized in response to the current transmitted between the supplycircuit and thewelding circuit. If desired, the actuating coil may beenergized from a shunt ili connected in series relation with the primarywinding of transformer 3. Relay I" is designed to open its contacts assoon as current begins to flow from the supply circuit 2 through thewelding transformer i.

To bias discharge device I to cut-oif after the contacts of relay IIIare opened, I connect a capacitance IS! in circuit with resistance I toimpress a negative voltage on the grid I.

The operation of the embodiment of my invention shown in the singlefigure of the drawing will be explained by considering the system whenit is operating to transmit current to the welding circuit I during apredetermined interval of time. Initially, switch 6 is closed Closure ofthis switch supplies current to the cathode heating elements 01' thevarious electric discharge devices and effects energization of actuatingcoil i 01 of the time delay relay I08. After a predetermined interval oftime which permits the cathodes to assume safe operating temperatures,relay I" closes its contact ill. The welding operation may then beinitiated by closure of switch II which energizes coil 82 of relay ll,electing closure of its contacts 84 and opening of its contacts Ii.Operation of relay ll also closes relay ill.

When contacts I! of relay II are opened, the discharge circuit forcapacitance I! is also opened and a timing impulse or voltage isgenerated by the charging of capacitance 86 from the source of directcurrent 53. The duration of this timing impulse, or a predeterminedportion thereof, determines the period of energization of the weldingcircuit l. The timing voltage which is produced by circuit 42 rendersthe discharge devices I and II conducting for a predetermined number ofcycles of voltage of the supply circuit. These discharge devices areconnected to operate in a leading and trailing relationship and transmita predetermined number of cycles of alternating voltage to the controlgrids ll of the electric discharge devices I! and II.

Prior to the application of the alternating voltages to control membersI! by coupling discharge devices I and I1, discharge devices I! and IIhave been maintained non-conducting due to the biasing potentialsimpressed on these grids by means of secondary windings 21 and 2|,respectively, of transformer 20. The voltages impressed on grids I! ofdischarge devices I! and IS by secondary windings l6 and II are notsufficient in magnitude of themselves to overcome the effect of thebiasing potentials, but when combined with the voltages of peaked waveform produced by secondary windings 40 and II of transformer II aresufllcient to render the electric discharge devices l2 and II conductingfor the number of half cycles of conduction established by electricdischarge devices I and II. In order to render the discharge devices I!and I3 conducting, the voltages derived through transformer 34 and thevoltages of peaked wave form must appear coincidentally in order toovercome the effect of the biasing voltages.

Upon being rendered conductive, the discharge devices I2 and il transmitimpulses of current alternately to control members I of electric valvemeans I and I, thereby rendering these electric valve means conductingalternately to transmit alternating current to the welding circuit i.

The amount of current transmitted to welding circuit I that is theeflective or R. M. 8. value, is determined by the time during the halfcycles of voltage of circuit 2 at which th electric valve means I and 5are rendering conducting. As the times at which the electric valve means4 and I are rendered conducting are advanced towards the zero pointduring the respective positive half cycles of anode-cathode voltage, theefiective value of current transmitted to the welding circuit isincreased and, conversely, at the times at which the valves are renderedconducting are retarded, the effective value is decreased. In otherwords, the effective value of current is a function of the angle orphase displacement between th zero value of the respective positive halfcycles of anode-cathode voltage and the time during the positive halfcycles at which the valves are rendered conducting.

The control circuit III and the associated apparatus function to controlthe phase relationship of the voltages of peaked wave form produced bysecondary windings ll and II of transformer ll relative to the voltageof supply circuit 2, thereby maintaining the load current at asubstantially constant value. The effective impedance of winding III oftransformer H6 is controlled in response to load current, or in responseto the current which is transmitted between the supply circuit and thewelding circuit to vary the phase of the alternating voltage supplied toprimary winding 28 t transformer 38 relative to the voltage of circuit2, thereby controlling the phase of the voltages of peaked wave form.

Electric discharge devices HI and I22 control the amount of currentwhich is transmitted through secondary winding H8 and, hence, controlthe effective impedance of winding I II. The

amount of current transmitted by discharge devices I2I and I22 isdetermined by the potential impressedon grids I23, and this potentialvaries in response to the output voltage of rectifier I24, or inresponse to the amount of current transmitted between the supply circuitand the welding circuit.

Considering the operation of the control circuit Iii in detail, electricdischarge device I31 transmits variable amounts of unidirectionalcurrent through resistance I38, thereby controlling the potential ofgrids I28. If it be assumed that the load current or the currenttransmitted to the welding transformer 3 momentarily tends to increaseto a value above the desired value, the voltage appearing acrossresistance I21 correspondingly increases effecting a rise in potentialof grid HI and causing the discharge device I31 to transmit an increasedamount of current. Such action lowers the potential of grids I28,effecting a decrease in the amount of current transmitted throughwinding I I8 and consequently increasing the efiective impedance ofwinding III. The increase of the impedance of winding I I1 effects aretardation in phase of the alternating voltage supplied to primarywinding 58 of transformer 28, and accordingly retards the phase of thevoltages of peaked wave form produced by windings 48 and H. Because ofthis retardation in phase, the electric discharge devices I2 and I5 andthe electric valve means 4 and I are rendered conducting at later timesduring the respective positive half cycles of applied anodecathodevoltage and, consequently, the eflective value of current transmitted towelding circuit I is decreased. In this manner, the load current or thewelding current is lowered to the predetermined value. Conversely, thesystem operates to raise the load current to the desired value if theload current tends to decrease to a value below the desired value.

The electric discharge device I45 serves to control the operation of theelectric discharge devices I2I and I22 during the initiation of each 7period of energization of the welding circuit I.

Immediately prior to the application of current to the weldingtransformer I, relay I58 is in the deenergized position efiectivelyconnecting resistances I48 and I49 in the system. The voltage impressedon grid I48 is sufllciently positive to maintain discharge device I45partially conducting, and as a result the voltage impressed on grids I23is maintained at a value so that discharge devices HI and I22 arepre-set to transmit current of a value slightly below the normaloperating point. This action simulates the operation that would beobtained if the current were slightly too large in the welding circuit.Thus the phase control is set below its normal current setting at thestart of the welding operation. As soon as the weld is initiated, thenormally closed contacts of relay I58 are opened and the grid I48 ofdischarge device I45 is lowered to a negative value determined by thevalue of the capacitance I52 and resistance I48. By the properadjustment of the constants of this circuit, discharge device I45 may bebiased to cut-oi! at approximately the same time the voltage acrossresistance I21, which represents the current signal, has had time tobuild up, and

the discharge device then proceeds to take over its regulating functionto! maintain constant current. The circuit I3I establishes a maximumlimit of the current transmitted to the welding circuit, or, viewed inanother manner, establishes the minimum phase displacement between theresultant voltage impressed on grids I! or discharge devices I2 and I8during the starting operation.

The period 01' energization of the welding circuit I is determined bythe timing voltage produced by timing circuit 42. When the timingvoltage decreases to a magnitude insuflicient to render dischargedevices and 81 conducting, the period of energization of the loadcircuit is terminated.

The system 'may be re-set by opening switch II which deenergizesactuating coil 82 of relay I5 and closes the discharge circuit forcapacitance 58. Upon subsequent closure, of switch 8i, a timing voltageis again produced and the above sequence of operation is repeated.

While I have shown and described my invention as applied to particularsystems pt connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member foreflecting energization of said load circuit for a predetermined numberof half cycles of voltage of said supply circuit, excitation means forimpressing on said control member a voltage which is variable in phasewith respect to the voltage or said supply circuit, said excitationmeans comprising a phase shifting circuit including an electricdischarge device having a grid, means responsive to the currenttransmitted between said supply circuit and said load circuit forvarying the potential of said grid to maintain said currentsubstantially constant, and means responsive to said current forcontrolling said discharge device andfor limiting the phase displacementof said variable phase voltage with respect to the voltage of saidsupply circuit.

2. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member, excitationmeans for controlling the energization of said control member to rendersaid electric valve means conducting for a predetermined number of halfcycles of voltage voltage on said control member to control the currentconducted by said valve means, means responsive to the current suppliedto said load circuit for varying said voltage over a predetermined rangeto maintain the current supplied to said load circuit substantiallyconstant, means for energizing said control member with a predeterminedvoltage within the limits of said range, and means for rendering saidlast mentioned means effective during periods of deenergization of saidload circuit to prevent said means responsive to load current fromenergizing said control member with a voltage corresponding to the limitof said range at the beginning of periods of energization of said loadcircuit.

3. In combination, a supply circuit, a load circuit, electrictranslating apparatus connected between said circuits and comprisingelectric valve means having a control member, control means forcontrolling said translating apparatus, means responsive to the currenttransmitted between said supply circuit and said load circuit forcontrolling the operation of said control means, preset means forinitiating a predetermined energization of said load circuit, and meansresponsive to the actual flow of current between said supply circuit andsaid load circuit for preventing operation of said preset means.

4. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member, excitationmeans for controlling the energization 01 said control member to rendersaid electric valve means conducting for a predetermined number of halfcycles 0! voltage of said supply circuit, means for controlling saidexcitation means to maintain the current transmitted to said loadcircuit substantially constant by varying the voltage oi said controlmember over a predetermined range, and means for energizing said controlmember during periods oi deenergization of said load circuit with apredetermined voltage intermediate the limits of said range to preventsaid last mentioned means from effecting energization of said controlmember in accordance with load current during periods of deenergizationof said load circuit 5. In combination, an alternating current supplycircuit, a load circuit, electric translating apparatus connectedbetween said circuits and comprising electric valve means having acontrol member, excitation means for controlling the energization ofsaid control member to render said electric valve means conducting for apredetermined number of half cycles 0! voltage of said supply circuit,said excitation means comprising means for impressing on said controlmember a voltage of variable phase relation with respect to the voltageof said supply circuit and comprising an electric discharge device,current responsive means for controlling said discharge device tomaintain the current transmitted to said load circuit at a substantiallyconstant value, means for controlling said discharge device to effectenergization of said control member in accordance with a predeterminedvalue of current in said load circuit prior to and during the initiationof current flow to said load circuit, and means responsive to thecurrent of said load circuit for rendering said last mentioned meansineffective.

6. In combination, a supply circuit, a load circuit, electrictranslating apparatus connected between said circuits and comprisingelectric valve means having a control member, excitation means forcontrolling the energisation of said control member for rendering saidelectric valve means conducting for a predetermined interval of time,said excitation means comprising means for supplying a control voltageto said control member for controlling the current transmitted to saidload circuit, means responsive to the current transmitted between saidsupply circuit and said load circuit ior controlling said last mentionedmeans, preset means for establishing a predetermined degree ofconductivity of said electric valve means, and means responsive to theactual flow of current between said supply circuit and said load circuitfor preventing operation of said preset means.

7. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member ioreffecting cnergization of said load circuit for a predetermined numberof half cycles of voltage oi said supply circuit, excitation means forimpressing on said control member a voltage which is variable in phasewith respect to the voltage of said supp circuit, said excitation meanscomprising a phase shifting circuit including an electric dischargedevice having a grid, a second electric discharge device {or controllingthe potential of said grid. means responsive to the current transmittedfrom said supply circuit to said load circuit !or controlling theconductivity of said second discharge device and for controlling thepotential of said grid to maintain the load current at a substantiallyconstant value, and means for establishing initially a predeterminedmaximum conductivity of said electric valve means upon initiation ofeach period of energization of said load circuit.

8. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member foreffecting energization of said load circuit for a predetermined number0! half cycles or voltage of said supply circuit, excitation means forimpressing on said control member a voltage which is variable in phasewith respect to the voltage of said supply circuit, said excitationmeans comprising a phase shitting circuit including an electricdischarge device having a grid, means [or controlling the potential 01'said grid in response to the current transmitted between said supplycircuit and said load circuit comprising a second electric dischargedevice having a grid, a third electric discharge device, said second andsaid third discharge devices being connected in parallel, meansresponsive to said current for controlling the conductivity of saidsecond discharge device thereby controlling the potential 01' the gridof the first mentioned discharge device, and means responsive to thecurrent transmitted between said supply circuit and said load circuitfor controlling the conductivity of said third discharge device to limitthe operation of said phase shifting means.

9. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member foreii'ecting energization of said load circuit for a predetermined numberoi halt cycles voltage at said supply circuit, excitation means forimpressing on said control member a voltage which is variable in phasewith respect to the voltage of said supply circuit, said excitationmeans comprising a phase shifting circuit including an electricdischarge device having a grid, means responsive to the currenttransmitted between said supply circuit and said load circuit includinga rectifier for producing a unidirectional Voltage the magnitude orwhich varies in accordance with said current, means connected betw ensaid grid and said rectifier for controlling the potential of said gridand comprising a second electric discharge device having a grid thepotential of which varie in accordance with said unidirectional voltage,a third electric discharge device connected in parallel with said seconddischarge device and connected to the grid of the first mentioneddischarge device, and means responsive to the current transmittedbetween said supply circuit and said load circuit for limiting thepotential impressed on the grid of the first mentioned discharge deviceduring the initiation of each period of energization of said loadcircuit.

10. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member foreflecting energization of said load circuit for a predetermined numberof half cycles oi voltage of said supply circuit, excitation means forimpressing on said control member a voltage which is variable in phasewith respect to the voltage of said supply circuit, said excitationmeans comprising a phase shifting circuit including an electricdischarge device having a grid, means responsive to the currenttransmitted between said supply circuit and said load circuit includinga rectifier for producing a unidirectional voltage the magnitude ofwhich varies in accordance with said current, means connected betweensaid grid and said rectifier for controlling the potential of said gridand comprising a second electric discharge device having a grid thepotential of which varies in accordance with said unidirectionalvoltage, a third electric discharge device connected in parallel withsaid second discharge device and connected to the grid oi the firstmentioned discharge device, and relay means responsive to the currenttransmitted between said supply circuit and said load circuit forcontrolling the conductivity oi said third discharge device to limit thephase displacement between said variable phase voltage with respect tothe voltage 0! said supply circuit during the initiation of each periodoi energization or said load circuit.

11. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member, anexcitation circuit for energizing said I control member including meansfor eflecting energization of said load circuit for a predeterminednumber of half cycles of voltage of said supply circuit, meansresponsive to load current for varying the voltage of said controlmember to vary the instant of initiation of conduction of said electricvalve means over a predetermined range and thereby to maintain said loadcurrent substantially constant, means for establishing an electricalquantity corresponding to s, predetermined instant within said range,and means for selectively rendering said last two mentioned meanseflective during period of energization and deenergization of said loadcircuit to limit the amount or phase advance oi! the instants at whichthe voltage impressed on said control member exceeds the criticalvoltage oi said valve means during periods 01' deenergization of saidload circuit.

12. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising electric valve means having a control member, means forenergizing said control member to determine the periods of energizationand deenergization of said load circuit, means for energizing saidcontrol member to control the instant in the anode-cathode voltage ofsaid electric valve means that said valve mean is rendered conductivecomprising means responsive to the current transmitted to said loadcircuit for varying said instant over a predetermined range, means forestablishing a predetermined energization of said control membercorresponding to an instant oi initiation of conduction intermediate thelimits oi said range, and means for selectively impressing the outputoi. said current responsive means and said electrical quantity on saidcontrol member to regulate said valv means in accordance with the loadcurrent during periods or energization and in accordance with saidelectrical quantity prior to each of said periods of energization.

ORRIN W. LIVINGSTON.

